*{
    margin: 0;
    padding: 0;
}
.clearfix:before,
.clearfix:after{
    display:block;
    clear:both;
    content:"";
}
.one{
    width: 1200px;
    margin: 0 auto;
}
.two{
    float:left;
    height: 100px;
    background-color: aqua;
    width: 30.333333%;
}
body{
    background-color: cornflowerblue;
}
@media (max-width:600px) {
    .one{
        width: 90%;
    }
    .two{
        width: 100%;
    }
    body{
        background-color: hotpink;
    }
}